Eccentric tensioners are used to apply a load to power transmission belts, which includes synchronous belts or toothed belts. For example, toothed belts are used on engine cam drives for power transmission and timing purposes. A tensioner is used to apply a proper belt load which in turn assures proper operation of the belt drive system of which the tensioner and belt are a part.
Such tensioners generally comprise a torsion spring and an eccentric pivot arm which creates a lever arm to apply a spring load to the belt.
During the operating life of an engine a toothed belt will slightly change length due to wear and other factors. This condition must be accommodated by the tensioner.
In addition, during load reversals, for example during engine deceleration, the tensioner must be able to prevent the belt from becoming unduly slack which can lead to a condition called “ratcheting” where the belt can “jump” across the teeth of sprockets in the system. This can lead to catastrophic changes in the engine timing and premature failure of the belt.
Ratchet and pawl systems are used to prevent tensioner pivot arms from excessive recoil during load reversals. Once released the ratchet and pawl systems cannot be relocked.
Representative of the art is U.S. Pat. No. 4,808,148 (1989) to Holtz which discloses a belt tensioning device includes a resilient coupling which interconnects an idler pulley hub and a stationary mounting member. A ratchet and pawl mechanism interconnects the hub and the stationary mounting member to prevent the belt from overcoming the biasing force of the tensioning device during high belt loads. A resilient biasing element such as an elastomeric element is located between the ratchet and pawl mechanism and the stationary mounting member to allow limited movement of the idler pulley hub away from a belt in order to relieve belt tension such as caused during thermal expansion of an engine block.
What is needed is a tensioner having a relocking stop mechanism that upon release allows the pivot arm to move from an installation position to an optimum operating position, which stop mechanism also prevents the pivot arm from moving in a reverse direction beyond a predetermined range during load reversals in a belt drive system, which relocking stop mechanism can be relocked to the installation position for belt replacement. The present invention meets this need.